Visual acuity has been the single most important parameter in measuring performance of human vision for over 150 years. Despite of its importance, visual acuity is almost useless for diagnosis of vision symptoms because it only measures vision performance with one specific task relating to visual resolution.
It is well-known that people can suffer from a host of night vision symptoms even though their visual acuity is 20/20 or better. This is particularly true for eyes after refractive surgeries. Surgical procedures can introduce unwanted high-order aberrations that are not correctable with conventional lenses.
Night vision symptoms are often referred as glare, halo, ghost images, and starburst. Even though night vision symptoms may not affect visual acuity, they can impair vision and make it dangerous for driving at night. It is unfortunate that vision of symptomatic eyes has never been properly cared because there is still no clinical means for specifying night vision symptoms.
Wavefront technology measures the total aberration in the eye including focus error, astigmatism, coma, spherical aberration, and a host of other high-order aberrations. It is often suspected that high-order aberrations contribute to most aberration-induced symptoms.
FIG. 1 shows a schematic diagram for a typical wavefront system using a Hartmann-Shank wavefront sensor. (Aberrations in the eye can also be measured with other devices like the ray tracing aberrometers, the Talbot Interferometry based aberrometer, and the phase retrieval method.) A fixation system (110) assists the tested eye in stabilizing its accommodation and in maintaining the view direction. An illumination light source (120) generates a compact light source to reflect off mirror (BS2) and shine on the eye's retina as the probing light. The probing light is diffusely reflected by the retina, from which a distorted wavefront is formed at the eye's cornea plane. An optical relay system (130), consisting of lenses (L1) and (L2), relays the outgoing wavefront from the eye and reflected off of mirror BS1 to the plane of a lenslet array. A Hartmann-Shack wavefront sensor (140), consisting of a lenslet array and an image sensor, produces a wavefront sensor image as an array of focus spots. An image analysis module (150) detects the focus spots and calculates the wavefront slopes, from which the wavefront is reconstructed by a wavefront estimator (160). From the eye's wavefront aberration, a vision diagnosis module (170) provides qualification of the eye's optical defects as well as the eye's optical quality, which provides the basis for a vision correction diagnosis.
Specifying and determining night vision symptoms from aberrations in the eye has not been possible because of at least two fundamental issues. First, night vision symptoms are not clinically measurable so far and we have little information about the true nature of night vision symptoms. Second, aberrations are optical defects in the eye and there is a missing link between aberrations in the eye and true performance of human vision.
In light of the forgoing, it is readily apparent that a need exists in the art to provide methods to link vision symptoms to image blurs caused by aberrations, to make vision symptoms measurable with specifically-designed vision tests, and to reduce vision symptoms by changing the total aberrations in the eye.